Cloud computing company Latisys Inc. is preparing to make about 40 hires this year, many of them at its Ashburn campus, as part of a national expansion fueled by a mix of equity and debt.

Latisys, which also operates data centers in Chicago, Denver and Irvine, Calif., has raised a quarter-billion dollars since 2007, allowing it to rapidly grow in both head count and infrastructure, said CEO Peter Stevenson.

The company ended last year with a staff of 157. Stevenson expects that number to hit just shy of 200, and possibly more, by the end of 2012. The new positions include sales, network and systems engineers, and technical personnel who can handle customer inquiries and problems.

Like its counterparts in the industry, Englewood, Colo.-based Latisys is benefiting from the general shift of business and government applications to the cloud.

The company handles a wide range of information technology outsourcing services, from any combination of storage, backup and security to complete managed hosting, which means a customer pays a monthly fee to have Latisys handle all of its storage and network security requirements.

Latisys plans to add 72,000 square feet to four data centers. Its Ashburn data center will take on 26,000 square feet, making it the biggest beneficiary of growth plans.

“We are seeing that continuation of demand,” said Stevenson, who would not disclose the company’s revenue. “This is the kind of business where if you want to meet that demand, you have to continue to build.”

In December, Latisys secured a $155 million credit facility to pay for the moves, adding to an already considerable pile of capital it amassed in recent years. That brings total funding to $255 million since October 2007, with the equity piece coming from Boston-based Great Hill Partners LLC and New York-based Catalyst Investors.

It’s hard to understate the explosion of cloud computing in recent years, though different segments are growing faster than others. Globally, the overall cloud computing market is slated to hit $241 billion by 2020, up from $40.7 million two years ago, according to a Forrester Research report, “Sizing the Cloud,” released last year.

The infrastructure-as-a-service market, however, is actually at risk of leveling off as prices shrink even as adoption increases, according to Forrester.

Much of that growth is due to big cloud providers such as Amazon.com Inc., whose low-cost Elastic Compute Cloud (EC2) has become especially popular with startups that want to avoid the costs of buying and running their own IT hardware.

But a massive Amazon EC2 cloud outage last year — which temporarily knocked out websites for Reddit, Hootsuite and scores of other companies — actually has proved to be a boon to providers like Latisys, Stevenson said.

“Entrepreneurs that started out building their businesses on EC2 built their businesses to the point where they have enough customers on there, they have enough revenues on there — when the [outage] took place, they all started looking to go to more private managed solutions,” Stevenson said. “And that’s what we’ve seen.”